Page 13 - Length

Sometimes it is not necessary to give the exact number or
measurement, even if it is possible. For example: The annual
school fun walk has an exact distance of 5 km 346 m. If someone
asked you the distance of the fun walk, you will probably answer
(about) 5 km.

1. Discuss these questions with one or two classmates.

(a) When do you think it would be a good thing to round off a
number or a measurement?
(b) When do you think it is necessary to give the exact
number or quantity?

2. The newspaper said there were 30 000 people at the soccer
game. Do you think that is the exact number of people that
attended the game?

To round a number usually means to find a multiple of 10, 100
or 1 000 that is close to the number. We say that we round up or
down to the nearest 10 or 100 or 1 000.

Examples:

142 is closer to 140 than to 150, so 142 rounded to the nearest 10
is 140.
147 is closer to 150 than to 140, so 147 rounded to the nearest 10
is 150.
145 is the same distance from 140 and 150. “Halfway” numbers
are usually rounded up to the larger of the possibilities. So, 145
rounded to the nearest 10 is 150.

3. Round off to the nearest 10:
(a) 26 cm (b) 144 mm

(c) 1 231 m (d) 50 335 mm
(e) 6 km (f) 5 km

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